1. Field of the Invention
The invention relates in general to a document size detecting device, and more particularly to a device for automatically detecting document size using a matrix optical sensing unit as a sensor.
2. Description of the Related Art
Electronic products such as scanner, printer, facsimile machine and multi-function machine all need to use a document size detecting device. Therefore, the use of an appropriate document size detecting device is important to the electronic products.
Referring to FIG. 1, a top view of conventional document scanning is shown. In FIG. 1, the scanner at least includes a flatbed 110 and several inter-spaced sensors such as sensors 105, 106 and 107. The flatbed 110 can have standard documents of three different sizes such as A3, A4, and B5 disposed thereon. In FIG. 1, the three types of standard documents are respectively named the standard documents 101, 102 and 103. In order to automatically detect the size of the standard document, normally several infrared sensors such as the sensors 105, 106 and 107 are disposed under the flatbed 110. When the to-be-detected standard document 101 is placed on the flatbed 110, the sensor 105 is covered by the standard document 101, but the sensors 106 and 107 are not covered by the standard document 101, hence the standard document is determined to be the standard document 101. When the standard document 102 is placed on the flatbed 110, the standard document 102 covers the sensors 105 and 106 but not cover the sensor 107, hence the standard document placed on the flatbed 110 is determined to be the standard document 102. By the same token, the document is determined to be the standard document 103 when the standard document covers the sensor 105, the sensor 106 and the sensor 107 at the same time.
An extra sensor needs to be added for the scanner to determine another size. Therefore, the more sizes to be determined, the more scanners need to be installed. Consequently, not only the larger space will be needed, the manufacturing cost will be increased at same time. However, if the document is a non-standard document, the conventional scanners would not be able to determine the size of the non-standard document. Furthermore, the sensors are normally infrared sensors, which are easily interfered with by the surrounding light, severely affecting the determination of the document size by the infrared sensors. In order to reduce the interference coming from the surrounding light, a coding circuit is installed at the emitting end of the sensors and a decoding circuit is installed at the receiving end of the sensors. However, the manufacturing cost is increased accordingly. Besides, when the conventional sensor is used, the resolution level cannot be increased.